Low loss optical fibers are finding increasing application in plasma diagnostics, particularly when immunity to electromagnetic interference and wide bandwidth are required. The fibers normally serve to transmit a light pulse, generated in a radiation-to-light converter, to a remote photodetector. Under some conditions, Cerenkov light generated by relativistic electrons in the fiber itself suffices to characterize the radiation environment. An example of such a system is described in U.S. Pat. No. 3,984,332, issued Oct. 5, 1976. This disclosure is concerned with the more general case where the light is generated in a liquid or plastic scintillator.
In numerous applications where it is necessary to observe and characterize ionizing radiation the radiation detection system utilized can be thought of as comprising three basic functional units. First, the radiation is detected; second, a signal of some kind produced by the detector in response to the radiation is transmitted to a remote location; and third, the transmitted signal is utilized to produce a recording and/or display or is otherwise processed to provide information about the radiation. It is apparent that errors introduced into the system by any of the functional units will affect the ability of the system to accurately characterize the observed radiation.
The detection of radiation is commonly accomplished utilizing a transducer which responds to the radiation in a manner which can be used to generate an electrical signal corresponding to some characteristic of the radiation. The electrical signal is transmitted over electric cables, commonly coaxial cables, to a location remote from the transducer for processing. However, the transmission characteristics of coaxial cables are such that significant distortion of information can occur, particularly in pulses of duration shorter than about 5 nsec.
The advent of commercially available fiber optic wave guides, commonly called optical fibers, has stimulated interest in their practical application to intelligence gathering and transmitting systems. Since the fibers have inherently greater information-carrying capacity than coaxial cables, their use as signal-carrying means in place of coaxial cables is, potentially, very attractive. With respect to systems for detecting and transmitting intelligence regarding radiation, U.S. Pat. No. 3,984,332 to Melvin A. Nelson, Terence J. Davies, and John R. Morton, III, assignors to the assignee of the instant application, of interest. That patent, entitled "Radiation Detection System," is directed to a system wherein the optical fiber serves as both the detector and the transmission means. Cerenkov light generated in a light guide by charged particle radiation is transmitted along the guide to a remote location for processing.
The optical transmission and material dispersion characteristics of known fiber optic wave guides vis-a-vis the output characteristics of known transducers which convert radiation to light have impeded the development of practical systems wherein the optical fibers serve only as the transmission means. This has been particularly true when requirements of the radiation detection system combine wide bandwidth with long transmission lengths, i.e., bandwidths greater than about 50 MHz and lengths greater than about 300 m. Such practical systems require radiation-to-light converters having emission wavelengths long enough to minimize absorption in the fiber which varies approximately as 1/.lambda..sup.4 where .lambda. is the wavelength. In addition, where the radiation to be detected is a very fast transient pulse, such as occurs in connection with a nuclear explosion, it is necessary for diagnostic purposes that the decay time of the light emission be very short, less than a few nanoseconds for some purposes.
Presently available long wavelength fluors (500 to above 600 nm) have decay times in excess of about 15 ns. This places serious bandwidth limitations on a fluor-fiber system. On the other hand, commercial fluors which do have short decay times have emission maxima less than about 430 nm.
In copending patent application Ser. No. 949,163, filed Oct. 6, 1978, now U.S. Pat. No. 4,292,527, which is hereby incorporated into the disclosure by reference, there is described a radiation detection system which uses a radiation-to-light converter in combination with an optical fiber that transmits light produced by the converter to a remote location for recording, display and other processing steps. This disclosure also describes several fluors suitable for use in radiation detection systems which utilize optical fibers as a means to transmit information regarding the radiation. These radiation-to-light converters produce light having characteristics peculiarly matched to the transmission characteristics of optical fibers.
For wide bandwidth over extended transmission paths, long wavelength emission and short decay time in the scintillator are essential for optimal performance. While the exact scintillator parameters are dictated by a specific application, minimum requirements are considered to be 500 nm emission, a response (full width at half maximum, FWHM) to a delta function input of about 2 ns, and conversion efficiency comparable to conventional plastic scintillators. While progress has been made in developing such scintillators, as evidenced by the disclosure of patent application Ser. No. 949,163, a scintillator optimized for fibers is not yet commercially available.
This disclosure relates to a liquid scintillator system based on use of 5-amino-9-diethylaminobenz (a) phenoxazonium nitrate, commonly known as Nile Blue Nitrate. It provides temporal characteristics comparable to conventional "blue scintillators" in long wavelength emitting scintillators and provides relatively high efficiencies.